[3.13.y-ckt stable] Patch "bridge: use _bh spinlock variant for br_fdb_update to avoid lockup" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    bridge: use _bh spinlock variant for br_fdb_update to avoid lockup

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt23.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 91f3f74c87c46fffa0a5d4c396c42be85e7dfa97 Mon Sep 17 00:00:00 2001
From: Wilson Kok <wkok at cumulusnetworks.com>
Date: Fri, 5 Jun 2015 00:52:57 -0700
Subject: bridge: use _bh spinlock variant for br_fdb_update to avoid lockup

commit 1d7c49037b12016e7056b9f2c990380e2187e766 upstream.

br_fdb_update() can be called in process context in the following way:
br_fdb_add() -> __br_fdb_add() -> br_fdb_update() (if NTF_USE flag is set)
so we need to use spin_lock_bh because there are softirq users of the
hash_lock. One easy way to reproduce this is to modify the bridge utility
to set NTF_USE, enable stp and then set maxageing to a low value so
br_fdb_cleanup() is called frequently and then just add new entries in
a loop. This happens because br_fdb_cleanup() is called from timer/softirq
context. These locks were _bh before commit f8ae737deea1
("[BRIDGE]: forwarding remove unneeded preempt and bh diasables")
and at the time that commit was correct because br_fdb_update() couldn't be
called from process context, but that changed after commit:
292d1398983f ("bridge: add NTF_USE support")

Signed-off-by: Wilson Kok <wkok at cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
Fixes: 292d1398983f ("bridge: add NTF_USE support")
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/bridge/br_fdb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 62c444d..e5421e6 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -475,7 +475,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 			fdb->updated = jiffies;
 		}
 	} else {
-		spin_lock(&br->hash_lock);
+		spin_lock_bh(&br->hash_lock);
 		if (likely(!fdb_find(head, addr, vid))) {
 			fdb = fdb_create(head, source, addr, vid);
 			if (fdb)
@@ -484,7 +484,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
 		/* else  we lose race and someone else inserts
 		 * it first, don't bother updating
 		 */
-		spin_unlock(&br->hash_lock);
+		spin_unlock_bh(&br->hash_lock);
 	}
 }

--
1.9.1